research activities in 2007 - CSEM

ActiSmile – A Portable Biofeedback Device on Physical Activity
B. Gros, J. Solà I Caros, P. Theurillat, J. Krauss, U. Mäder • , H. Buchholz ••
Together with the Swiss Federal Office for Sports (BASPO) and the company ActiSmile SA CSEM has designed and developed a portable
biofeedback device to continuously monitor the physical activity of its user. The key technology resides in sophisticated signal processing methods
for multi-axis accelerometer sensor systems, including modern feature extraction, classification algorithms and low-power implementation on a realtime
platform.
Motion is an important modulator of vital human organic
functions such as respiration, heart cycle, blood oxygen
saturation. Physical activity is viewed as an important
component of a healthy lifestyle and the relationship between
physical activity and several known risk factors for chronic
diseases are well-known. Important information about human
health is expressed in human motion during day and night,
such as the daily relative percentages of walking or running
with respect to resting. These relative percentages can be
used as indicators of potential psychological disorders or
physiological pathologies. Accelerometry-based activity
monitors are widely used to capture objective information on
patterns and levels of physical activity. Although data
collection is relatively easy, data reduction and data
processing are challenging topics.
The company ActiSmile SA has mandated CSEM to design,
develop and implement a portable biofeedback device to
continuously monitor and promote the physical activity of its
user. The classification approach relies on the signals of a
multi-axis acceleration sensor system which are projected to
the breast vertical axis of the subject. Feature extraction is the
essential part of the processing prior to any classification task.
Features depend on the signals and the choice of a pertinent
small size of feature set improves the intersubject
classification accuracy. The design of the feature space in the
classification machine takes into account the final desired low
complexity algorithm in order to target a low-power and
portable application on a real-time platform. For this reason,
features derived from frequency or any other eigenfunction
transformed domain has been eluded. An extensive study on
the physiology of human motion has allowed the development
of a new set of proprietary features derived from the temporal
domain. The features are fed to classification stage. Being
aware that the final applications may require different
classification resolutions, a decision tree has been chosen as
the most appropriate classification strategy.
The ActiSmile device performs in real time the data
acquisition, feature extraction, classification and high-level
interpretation routine tasks. The output of the processing
stage corresponds to an activity class tag (namely: lying,
standing, walking, running), which is calculated every
5 seconds and stored within the FLASH memory of the
portable ActiSmile device. A high-level interpretation algorithm
calculates with the number of stored activity class tags the
user feedback. A SMILEY is fed back and displayed on the
LCD of the ActiSmile device, if the user has performed the
defined minimal physical activity according to the guidelines of
the World Health Organisation (WHO). Figure 1 shows the
portable ActiSmile devices which are worn either with a clip on
the thorax of the user or at the belt, or around the neck with a
lanyard. The ActiSmile device can be recharged via a
standard USB cable.
Figure 1: Portable ActiSmile device with USB version (left) and
wireless version (right).
The transmission of the stored activity class tags to a data
validation software can be performed either via an USB link or
wireless with a Bluetooth version, as shown in Figure 1. The
transmitted data can be validated under a Windows based
data visualization and calibration software. The trends of the
performed physical activity can be visualized on a daily,
weekly and monthly basis as shown in the graph of Figure 2.
Moreover, the data validation software provides a calibration
tool to program and individualize the portable ActiSmile device
with the personal data age, weight, sex and fitness level. The
calculation of the SMILEY feedback is adapted accordingly.
Figure 2: Windows based data visualization software, with the graph
of the performed daily physical activity (x-axis: time; y-axis:
percentage of performed physical activity).
The verification of the correct interpretation of the performed
physical activity with the ActiSmile devices has been validated
by the Swiss Federal Office of Sports. A pre-series of the
ActiSmile product was launched in October 2007 and a further
product enhancement is planned during 2008.
•
Institute of Sports Sciences, Federal Office of Sports (BASPO),
CH-2532 Magglingen; (www.baspo.admin.ch)
••
ActiSmile SA, Rathausstrasse CH-6340 Baar;
(www.actismile.ch)
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